Presently known systems of that type nevertheless suffer from the drawback in that the rotary motion of the electric adjustment motor is transmitted to the adjustment mechanisms via a common reduction gear unit and via clutches that are all situated close to the adjustment electric motor, further gearing possibly being located close to each adjustment mechanism.
The members for transmitting rotary motion which are coupled between the clutches and the adjustment mechanisms (flexible shafts or other transmission members) rotate relatively slowly, so they have to transmit large amounts of torque, thereby requiring the use of transmission members that are strong, and therefore expensive, bulky, and relatively heavy.
Also, the additional gearing disposed close to each adjustment mechanism increases the total weight to the system.
Document FR-A-2 558 871 discloses a vehicle seat adjustment system of the kind in question, which avoids the above-mentioned drawback by providing gear units distributed about the seat, in the vicinity of each adjustment mechanism, with each gear unit being suitable for coupling to the adjustment motor via at least one transmission member rotating at the same speed as said adjustment motor.
The adjustment system disclosed in that document includes a clutch and selection mechanism between the adjustment motor and the transmission members that are respectively coupled to the gear units, for the purpose of selecting which adjustment mechanism is to be actuated.
That clutch and selection mechanism is complex and fragile.